See the example

Challenge?

If anyone is up to the challenge, have a crack at getting the transparency working (note that this needs to be on a td and not a div - for which I've seen a fix already).

The long solution is to use border-color: #fff; - but it not as easy as that in my situation since I got lots of different colours to deal with, and it would (and probably will) require a lot of additional, conditional, CSS.